We propose 7 projects related to the general biology of melanoma and its precursor lesions. (1) Identify the specific cutaneous phenotypes indicating a patient is at increased risk for melanoma. (2) Establish the statistical risk of melanoma in patients with the heritable and sporadic large atypical nevus syndrome (LANS). (3a) Study by regression analysis 27 prognostic parameters in melanoma. (3b) Determine the types and incidence of the precursor lesions of melanoma. (3c) Study comparatively the host response to primary and metastatic melanomas. (3d) Study comparatively matched cases of fatal and non-fatal melanoma. (4) Study the fine structure of lesions confused with melanoma. (5) Study the efficacy of 5-FU in treating dysplastic nevi. (6) Carry out psychosocial and psychobiological studies during the course of melanoma. (7) Computerize our entire clinical and histologic data base of melanoma cases.